A conventional rectilinear sliding bearing comprises a rail to be fixed to a fixing section of a machine or the like which has axially-extending rolling surfaces on which rolling elements roll, a slider movable along the rail which has a load zone including load rolling surfaces provided in confronting relation to the rolling surfaces of the rail and a no-load zone for connecting both ends of the load zone, the two zones defining endless tracks, and a number of rolling elements for bearing loads between the load rolling surfaces of the slider and the rolling surfaces of the rail while circulating through the endless tracks. In practice, for example, a plurality of such rails are laid in parallel on the fixing section, and a moving body such as a table is connected to the slider.
This type of rectilinear sliding bearing can possess the so-called automatic adjusting function (of reducing a moment load acting on the bearing) by making the angle of contact of the load rolling surface with the rolling element close to the angle of contact of an outer ring with a ball in front combination form of an angular contact ball bearing (which is one type of rotary bearing) to short the distance between two working points appearing when loads act on the bearing. On the other hand, the bearing can also possess the so-called automatic aligning function (of causing a moment load acting on the slider to be effectively absorbed between a bearing race and a block) by dividing the slider having the automatic adjusting function into a substantially cylindrical bearing race having endless tracks and a block having a table attaching surface which is fitted on the bearing race.
In these rectilinear sliding bearings, even when there is the attaching error of the rail relative to the fixing section (such as the error in parallelism or, level of two or more rails), the slider can be smoothly moved and the moving body can be rectilinearly guided with accuracy.
However, where the rail has some vertical waving resulting from the disorder of the surface of the fixing section on which the rail is laid, improper tightening of rail fixing bolts, etc., the slider moving along such a rail undergoes pitching in the moving direction, so that the machining accuracy of a machine tool, for example, mounted on the moving body is degraded.
To overcome such a defect, Japanese Patent Laid-Open No. 62-188636 has proposed a rectilinear guide device. This, as shown in FIGS. 21 and 22, is characterized in that a gap retaining washer (c) is interposed between a slider (a) and a moving body (b) to retain a gap between them, and an attaching bolt (d) is passed through the gap retaining washer (c) and screwed into the slider (a) to connect the slider (a) and the moving body (b) together, whereby the structural error of rail (e) can be absorbed or moderated by means of the relative displacement between the slider (a) and the moving body (d) that results from the elastic deformation of the attaching bolt (d) (specifically, by a sliding contact action between an arcuate convex surface (f) of the gap retaining washer (c) and an arcuate concave surface (g) of the slider (a) or moving body (b)). In this rectilinear guide device, the pitching of the slider (a) is absorbed between the slider (a) and the moving body (b); therefore, the positional accuracy in movement of the moving body (b) is enhanced to overcome the foregoing defect.
However, the proposed rectilinear guide device has other defects. First, since the sliding contact action between the gap retaining washer (c) and the slider (a) or moving body (b) is utilized, when the amount of tightening of the attaching bolt (d) is large or the moving body (b) suffers a large load/weight, the coupling force between the slider (a) and the moving body (b) becomes strong, and a large frictional force acts between the arcuate convex surface (f) and the arcuate concave surface (g), whereby the function of relative displacement owing to sliding contact cannot be exerted sufficiently.
Second, if the area of sliding contact is decreased for the purpose of sufficiently exerting the function of relative displacement owing to sliding contact, a concentrated load acts on the slider (a) and the moving body (b), whereby the individual components (a), (b) tend to be deformed or damaged.
In view of the foregoing defects, it is an object of the present invention to provide a rectilinear sliding bearing of high reliability which can effectively absorb or moderate the attaching error of a rail.
It is another object of the present invention to provide a method of assembling a rectilinear sliding bearing which makes it possible to accomplish the first object.